Scent and Human Psychology

The role of sensory organs in human life is quite significant. Seeing, hearing, touching, tasting and smelling are activities we perform at every stage of our lives. These actions, which have become routine in our daily lives, occur as a result of complex processes in our brain.

However, among these, the sense of smell occupies a much more special place. Research on the sense of smell shows that smelling is the oldest sense. It has been determined that smell evolved before our other senses to enable people to react to chemicals in their environment. To see, the human eye contains four different receptors and these receptors convert light into electrochemical language so that our brain can perceive it. The sense of touch, like the sense of sight, has different receptors and these receptors enable the perception of cold, heat or pain. However, the sense of smell is quite different from other types of senses in this regard. Because humans have at least 1,000 different smell receptors and these receptors change depending on the differentiation of smells that the person has become accustomed to throughout their life or smells they have never encountered before. As a result of this differentiation, people can distinguish many types of smells. Another difference of the sense of smell from other senses can be described as the method of description. We can describe any object we see by saying what it looks like, its shape, size and color, but describing an object we smell is more difficult compared to describing an object we see. We can describe the smell of objects we smell by relating it to something else. For example, let us think of the moment when we smell the scent of a flower we love reaching our nose or when an unpleasant smell reaches our nose. We will not take long to notice these smells we love or dislike. However, from the second we breathe in that air, the brain will have performed many processes related to smell and will have enabled us to perceive the smell within seconds from the moment we breathed in that air. But how does this incredible mechanism work?

The Smell Mechanism

Smelling is a chemical sense because the stimulus is different chemicals carried in the air. First, the stimulating smell molecules in the air reach the smell cells in our nose as we breathe. Smell cells are located in two tissue areas at the top of the nasal passages. The function of these cells is to convert these molecules carried by air into electrical current, i.e., this is a kind of convection of chemicals. Smell cells or smell receptors are covered with mucosa, volatile molecules in the air dissolve in the mucosas and stimulate the smell cells below them. Smell cells trigger nerve currents going to the brain; these currents are evaluated as different smells in the brain. The nerve currents produced by smell cells go to the smell bulb located at the bottom of the brain. The smell bulb contains smell receptors that convert dissolved molecules into electrical signals. The nerve currents coming from the smell bulb are transmitted to the piriform cortex, which is the primary smell cortex. The piriform cortex converts volatile smell molecules in the air into smell sensations, i.e., it enables us to perceive different smells. Our brain performs all these processes so quickly that as soon as we breathe, we immediately perceive what the smell molecules in the air resemble.

Smell and Human Psychology Interaction

Although research on the interaction between smell and human psychology has gained popularity in recent years, in Turkish medical history, famous medical scholars such as Ibn Sina and Al-Biruni were aware of this interaction. In fact, these scholars used the rose in treating mental patients and observed that it opened the mind and strengthened memory. Indeed, a German research group found that subjects' levels of intelligence and perception increased after sleeping in a rose-scented room, and later a Turkish research group proved that mice fed with roses had strengthened memory. Mevlana Celaleddin Rumi's advice "Scent opens the eye of the heart" is not without reason. But how does this interaction occur? The sense of smell is undoubtedly an integral part of living beings' lives. Apart from the sense of smell being a sense that humans only use in their daily lives, it also contributes to human life cognitively. While the sense of smell was considered physiologically, we talked about many different smell receptors and how these receptors enable us to perceive smells. Smell receptors send signals to all points in the brain according to external stimuli received. This signal activates the relevant areas. Compared to other senses, the sense of smell goes directly to the brain because it evolved before other senses. The part of the brain responsible for processing smells, the Olfactory bulbus, is located just below the hippocampus region of the brain. The side-by-side positions of the Olfactory bulbus, where smell is processed, and the hippocampus in the brain led scientists in the past to think that the smell center was the hippocampus, but later research proved this information to be incorrect. The spatial relationship between the brain region where smell is processed and the hippocampus also shows the relationship of smell with the limbic system. The limbic system can be described as a region of the brain where humans' emotional and behavioral responses are formed. Within the limbic system there are many structures responsible for different functions and this system works not independently but in cooperation with other systems in the brain. The limbic system is found not only in humans but also in animals whose roots date evolutionarily to very ancient times. The brain system that enables animals to cope with their environment and other species in their surroundings is the limbic system. The limbic system is a system involving social behavior for humans and other species to sustain their lives.

In most species, the maintenance of social relationships relies on the importance of the sense of smell. The sense of smell is less important for the human species compared to other living organisms. However, based on information from the senses, the limbic system shapes human emotions and behaviors. The limbic system has many different functions. The hypothalamus, one of the important parts of the limbic system, has many different functions such as basic instinctive behaviors like eating and sexuality, behaviors that cause body arousal and regulating the hormonal secretion of the body.

The amygdala, another part of the limbic system, receives clues from the senses and associates these clues from the senses with emotions. Due to the connections of the hippocampus, a part of the limbic system, and the amygdala within the system, specific sensory inputs create memory relationships with emotions. For example, we receive emotional responses from the amygdala in response to certain smells we receive.

The amygdala is the origin point of emotional responses such as fear, anxiety and excitement created by the received smell in the individual. Additionally, it has been determined as a result of conducted studies that if the individual has a life event related to the received smell, the hippocampus provides the recording of this memory.

Research on the sense of smell has found that this sense plays a role in the processing of different cognitive processes. One of the cognitive variables affected by smell is memory. It is particularly closely associated with episodic memory, one of the components of long-term memory. Episodic memory can be defined as the memory that includes an individual's recollection of experiences, situations and important life events in their own life. Any life event can be remembered with sensory clues, i.e., a past event is based on the combination of relationships affecting more than one sensory area. The hippocampus, one of the parts of the limbic system, is associated with the retrieval of episodic memory.

Many conducted studies have concluded that the sense of smell has an effect on the process of retrieval of life events from episodic memory. With the identification of the effects of smell on human psychology, the psychological sciences have conducted more research on smell in the last ten years. In fact, the psycho-aromatherapy sub-branch of aromatherapy, which is connected with psychology, has gained acceptance in scientific circles. The aim in psycho-aromatherapy is for the person to achieve a specific emotional state with oils that provide vitality and relaxation.

Particularly in studies conducted on psycho-aromatherapy, it has been determined that with the inhalation of volatile oils through the nose, relevant places in the brain are stimulated to secrete hormones such as serotonin, endorphins and similar substances in the body, and the secreted hormones provide a feeling of relaxation and calmness as a result of the connection of nerve and body systems to each other. Furthermore, aromatherapy has effects on different psychological problems. Studies have reached the conclusion that aromatherapy reduces symptoms of anxiety disorders, depression, schizophrenia and similar illnesses. At the same time, its effect on symptoms seen in sleep disorders is also quite significant. In studies addressing sleep disorders, it was concluded that aromatherapy provided a positive increase in sleep quality. Ballard et al. (2002) examined the effect of scents on dementia patients in their study. As a result of the experiment conducted with a total of 71 participants over a period of 4 weeks, they found that lemon balm scent was an effective and reliable way to treat dementia and improve quality of life. Another study on smell and emotional state showed that pleasant scents improved the mood of women and men in midlife crisis and had an effect on alleviating women's complaints related to menopause. Research has been conducted on the effects of some specific scents on emotional state. In a study where pleasant scents such as lavender were presented, it was observed that lavender scent positively affected the mood of subjects while they performed a stressful task. In another study conducted, it was found that some scents such as lavender, orange, vanilla and jasmine positively affect emotional state and relax the person, while rosemary and mint scents have stimulating effects (Diego et al., 1998).

Looking at the historical process, in the Ottoman period, flowers were grown in many hospitals and their beauty and scent were used in the treatment of psychological illnesses. While this is the case and studies on the effects of scents on human psychology in Turkish history date back so far, modern science has given relatively recent weight to research in this field. There is much more work to be done and much more ground to be covered in this area.

Aromatherapy has been reported in literature to be used as an effective treatment method in many psychiatric illnesses such as dementia, Parkinson's, schizophrenia, sleep disorders and anxiety disorders. However, what must not be forgotten is that aromatherapy has a calming effect on the symptoms of the illness. In other words, aromatherapy should be considered within the scope of auxiliary tools (complementary medicine) in the treatment of these illnesses. In conclusion, senses have quite an important place in shedding light on the complex human brain and the complex human psychology connected to it. Among these, the sense of smell is one of the most effective sensory organs on human psychology. Particularly with studies conducted in this field, the importance of smell on human psychology will be understood even better in the coming years.

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